1. Field of the Invention
This invention relates to a sound absorbing member comprised of a cheap sound insulation structural body having high performances, and more particularly to a sound absorbing member having improved sound absorbing performance, sound insulating performance and economical efficiency and a high contribution to social welfare by positively utilizing recycled polyethylene terephthalate (PET) materials.
The sound absorbing members according to the invention are particularly suitable as an interior sound absorbing member for automobile such as floor insulator, dash insulator arranged on a dash panel and the like.
2. Description of the Related Art
The invention will be described with respect to the dash insulator for the automobile used under severe restricting conditions among the sound absorbing members below. As shown in FIG. 1, the conventional dash insulator 2 locates on a surface of a dash panel 1 dividing an engine room E and a compartment R, and is provided with a sound insulating layer 3 and a sound absorbing layer 4, and serves to prevent transmission of noise from the engine room E to the compartment R.
As shown in FIG. 2, the dash insulator 2 arranged on the dash panel 1 is generally a multilayer structural body of the sound insulating layer 3 having a relatively high surface density such as polyvinyl chloride sheet, rubber sheet or the like incorporating a filler therein and the sound absorbing layer 4 of a porous material such as felt, polyurethane foam, nonwoven fabric or the like.
In the conventional dash insulator, noise from the engine room E is absorbed by the sound absorbing layer 4, while good soundproof performance is developed by a double sound insulating effect through the dash panel 1 and the sound insulating layer 3.
Recently, it has been confirmed that the sound insulating performance of the dash insulator largely changes in accordance with the adhesion to the dash panel 1. As a result, there are mainly used dash insulators in which a molded sound absorbing member exactly fitting to a surface shape of the dash panel is used as the sound absorbing layer 4. For example, fibrous sound absorbing members are manufactured by adding a resin binder to chemical fibers or natural fibers and shaping and pressing them under heating. As the resin binder, use may be made of thermoplastic resins such as polyethylene resin, polypropylene resin, polyester resin and the like or thermosetting resins such as phenolic resin and the like.
In this connection, U.S. Pat. No. 5,064,714 discloses an internal trim member for automobile in which a fiber assembly in the member is mainly formed by a filling method wherein fibers are blown in a mold together with air. In this method, however, the fibers do not easily come into details of the mold, so that it is required to use thick fibers (6-8 denier) having a relatively heavy weight for attaining complete filling. On the contrary, the use of fine fibers having a size of not more than 4 denier is required for giving high sound absorbing performances to the internal trim member, but these fine fibers are poor in the dispersibility and are unapplicable for the above method because the productivity and the sound absorbing performances can not simultaneously be established. Particularly, not less than 30% by weight of fibers having a size of not more than 4 denier, preferably not more than 2 denier should be included in the internal trim member for satisfying the sound absorbing performances, which is not attained by this method.
In the sound absorbing layer 4 for the conventional dash insulator, the felt or the like comprised of natural fibers is mainly used, so that the scattering of fineness is very large to bring about the ununiformity of sound insulating performance and hence it is difficult to constantly hold such a performance as a product.
Furthermore, the sound absorbing layer has the drawbacks that (i) the sound absorbing performance is poor because a great amount of fibers having a thick denier are existent, (ii) the sound absorbing performance is low in proportion to weight owing to the use of the resin binder, and the like.